Brothers Jasson and Bryan Monzon told Sky News they planned to pay thousands to a "coyote", an illegal people smuggler, to get them across the border and join their brother this year. They know they run the risk of failure or even of death.

Bryan said: "I'm always worried about what will happen on the way from here to the border. I'm always saying God will protect me.

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Gallery: Lone Migrant Children Left In Limbo

US authorities are struggling to cope with the numbers of lone children arriving as illegal immigrants

"We want to be together so we will do it."

The "coyotes" are doing brisk business with their networks through Guatemala and Mexico.

But some of those who have tried and failed to make it into the US have returned determined to persuade others not to follow.

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Santana Cano was robbed at gunpoint by a Mexican drugs cartel as he neared the border. His third attempt to reach the US, he says, was his last.

"I was crying because I saw children the same age as my son and they were travelling alone, saying their dad would pick them up at the border. I could never do that to my son.

"It is dangerous and I want the young people to understand that what I am saying is real. They need to listen."

Video:Children Risk Lives To Get To US

But when Santana spoke to pupils at a school in Huehuetenango, he found almost half of a class of 23 children wanted to make it to the US.

One who didn't was 15-year-old Karla Maldonado de Leon. Her cousin headed for the US and hasn't been heard from since. "Children should get an education and a visa before they go," she said.

The prospect of escaping poverty and violence and sending better wages back to their families remains a powerful motivation for youngsters.

Video:Governor: Send Back Immigrant Kids

George McCoy, recently deported from the US back to Guatemala, told Sky News: "They don't have money to survive. They want a better life."